This application is based on Japanese Patent Applications No. 2001-190313 filed on Jun. 22, 2001, and No. 2001-372915 filed on Dec. 6, 2001, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an adsorption-type refrigerating apparatus which can be suitably used for an air conditioner.
2. Description of the Related Art
As described in Japanese Patent Laid-Open Publication No. Hei. 11-37598, an adsorption-type refrigerating apparatus has a cooling capacity by evaporating a refrigerant such as water, and prevents an increase in an inner pressure (i.e., evaporating pressure) of an evaporator by adsorbing the evaporated refrigerant into an adsorbent to perform continuous evaporation in an adsorption step. The capability of adsorbing the refrigerant gradually decreases (i.e., gradually saturates) as the adsorption of the refrigerant proceeds. Generally, when the capability of adsorbing the refrigerant becomes saturated, the adsorbent is heated to remove the refrigerant from the adsorbent, thereby recycling the refrigerant in a desorption step. Subsequently, the adsorption step is performed by the use of the removed refrigerant.
For such steps, the adsorption-type refrigerating apparatus generally has at least two adsorbers. That is, there are first and second adsorbers provided with containers or the like in which adsorbents are contained, respectively. When the first adsorber is in the adsorption step, the second adsorber is in the desorption step. Alternatively, when the second adsorber is in the adsorption step, the first adsorber is in the desorption step. Therefore, the refrigerating apparatus is capable of continuously performing its cooling capacity (cooling capacity).
The cooling capacity of the adsorption-type a refrigerating apparatus is determined based on the amount of the refrigerant to be evaporated. More specifically, as shown in FIG. 4, the cooling capacity is determined based on a difference xcex94C between amount adsorbed C1 at the condition of the adsorption step, and amount adsorbed C2 at the condition of the desorption step. FIG. 4 shows an isotherm of a silicagel. In FIG. 4, the abscissa denotes the vapor pressure rate "psgr" (i.e., a relative humidity) which is the rate of the partial pressure of water vapor around the adsorbent to the vapor pressure of saturated water (refrigerant) at the temperature of the adsorbent. The amount adsorbed C is the mass of water adsorbed in the unit mass of the adsorbent.
The adsorbent generates heat when adsorbing the refrigerant (hereinafter, the heat is referred to as xe2x80x9cadsorption heatxe2x80x9d). The vapor pressure of saturated water at the temperature of the adsorbent increases as the temperature of the adsorbent increases, so the vapor pressure rate "psgr" decreases to cause the reduction in the amount adsorbed C. In the adsorption step, therefore, the adsorption of the refrigerant is performed while the adsorbent is cooled. The adsorbent is generally cooled by the outside air. Thus, when the outside air temperature Tam increases, the vapor pressure rate "psgr"1 in the adsorption step becomes smaller, and the amount adsorbed C1 in the adsorption step becomes smaller.
On the other hand, in the desorption step, the adsorbent after completing the adsorption step is heated. When the outside air temperature Tam increases, the temperature difference between the outside air and a heat source for the heating becomes smaller. Therefore, the vapor pressure rate "psgr"2 in the desorption step increases, and the amount adsorbed C2 in the desorption step increases. Accordingly, the increase in the outside air temperature Tam leads to the decrease in the amount adsorbed C1 in the adsorption step and also leads to the decrease in the amount adsorbed C2 in the desorption step. Consequently, the amount of the refrigerant which can be evaporated decreases, so that the cooling capacity of the adsorption-type refrigerating apparatus can be decreased.
The inventor of the present invention calculates the difference between the amount adsorbed C1 of refrigerant in the adsorption step and the amount adsorbed C2 of refrigerant in the desorption step, with the assumption that the temperature of the heat source for the heating is 90xc2x0 C. and the vapor temperature is 10xc2x0 C. As a result, using a typical silica gel as the adsorbent, there was no difference between them when the outside air temperature becomes about 45xc2x0 C., or higher. In such a case, therefore, the adsorption-type refrigerating apparatus will be substantially stopped.
In view of the foregoing problems, it is an object of the present invention to provide an adsorption-type refrigerating apparatus capable of having cooling capacity even when the cooling temperature of an adsorbent increases.
According to the present invention, in an adsorption-type refrigerating apparatus, an adsorber has therein an adsorbent for adsorbing evaporated refrigerant in an adsorption step, and for releasing the refrigerant adsorbed in the adsorbent by heating in a desorption step. The adsorbent has a temperature-dependent characteristic in which an amount adsorbed in the adsorption step is larger than an amount adsorbed in the desorption step even when a vapor pressure rate in the adsorption step is equal to or smaller than a vapor pressure rate in the desorption step. Accordingly, even when the vapor pressure rate in the adsorption step is equal to the vapor pressure rate in the desorption step, the amount adsorbed in the adsorption step is different from the amount adsorbed in the desorption step. Therefore, even when the cooling temperature of outside air for cooling the adsorbent increases, a sufficient cooling capacity can be obtained. In addition, a difference between the amount adsorbed in the adsorption step and the amount adsorbed in the desorption step can be made larger. As a result, the cooling capacity of the adsorption-type refrigerating apparatus can be improved while the amount of the adsorbent filled in the adsorber can be made smaller, even when the cooling temperature of the adsorbent is high.
Preferably, a ratio of an adsorption heat generated in the adsorbent to an evaporation latent heat of the refrigerant is set in a range between 1.2 and 1.6. Therefore, the refrigerant adsorbed in the adsorbent can be readily released at a relative low temperature (e.g., 100xc2x0 C.) without adding an additional device.